Not AND (NAND) flash memory is a non-volatile solid state memory that does not need power to maintain data stored in the memory. Such feature makes NAND memory a popular storage solution for a variety of devices, such as removable storage cards, cell phones, MPEG-1 Audio Layer 3 (MP3) players, and other devices. Accessing a NAND memory may include programming (or writing) a page of data, reading a page of data, and erasing a block of data. A device may access a NAND memory with standard NAND commands. For example, a NAND memory may respond to a set of NAND commands such as read status, program page, page read, and other commands.
A limitation of NAND memory is the erasure of data. The application of an erase pulse to memory cells associated with a NAND memory that are not programmed (i.e., a zero logical state) drives the memory cells into a deep erased state. The erase pulse may therefore result in over erased memory cells that can cause errors in programming. To overcome such limitation, an extra programming operation of all memory cells to a one logical state is conducted before an erase operation. Such extra programming operation before an erase operation lengthens the time period of an erase operation.
Additionally, another limitation of NAND memory is that NAND memory does not allow changes to bit values at random. Thus, to perform a write operation, the NAND memory requires an erase operation before the write operation. Such additional erase operation before a write operation lengthens the time period of a write operation. As a result, there is a need for continuing efforts to improve a NAND memory system.